Method of producing phosphorus oxychloride



Oct. 9, 1951 P. DUPONT METHOD OF' PRODUCING PHOSPHORUS OXYCHLORIDE Filed May 14, 1947 INVENTOR.

Patented Oct. 9, 1951 METHOD 0F PRoDUoING rHosPHoRUs OXYCHLQRIDE Paul Dupont, .Pai-is, France, assigner to Societe Anonyme des Manufactures des Glaces et Produits Chimiques de Saint-Gobain, Chauny & ,l

Cirey, Paris, France Application May 14, 1947, Serial No. 748,099 In France ,August 16, 1944 section 1, Public Law 69o, August s, 194s Patent expires August 16, 1964 3 Claims.

This invention relates to the manufacture of phosphorous oxy-halides and particularlyl to the manufacture of phosphorous Oxy-chloride by an improvement over the known process of subvjecting an ortho phosphate or a meta phosphate of calcium to the reaction of chlorine in the presence of a reducing agent, such as carbon. Phosphorous Oxy-chloride is a particularly valuable member of the class of compounds that can be made by this process and the invention will be described with particular relation thereto.

This invention includes an improvement in process and an improvement in apparatus, over the known method wherein the basic reaction is expressed by the equation be replaced by calcium meta phosphate, the reaction is expressed by the following equation:

and the quantity of chlorine consumed in producing a given quantity of phosphorous Oxy-chloride is only two-thirds of that which is required when starting from tri-calcium phosphate. Hence, operating in accordance with this reaction may be more advantageous.

The present invention comprises an improved processy for the manufacture of phosphorous oxychloride, utilizing reactions'of the type indicated above. In a preferred embodiment the calcium chloride formed at the start of the reaction is utilized as a source of heat by passing an electric current through it.

As a preliminary step, in order to initiate the reaction, the temperature in the reaction chamber is raised to about 800 C., by the aid of any kind of associated heating means, so that the calcium chloride formed passes into the liquid state and accumulates at the bottom of the reaction chamber, which is provided at this level with current-supply means. The heating meansk in the drawing is a pair of electrodes 9. Initial heating can be begun by admitting mixed carbon 2 f f and CaClz between the electrodes to carrythe current until the molten pool forms.

It is an advantage of my discovery that a relatively slow rate of generation of heat in the heating resistance thus constituted by the calcium chloride is sulcient to compensate for the heat losses of the process and apparatus and to maintain the temperature at about 800 C. The chlorine gas admitted at the base of the furnace through tuyres 8 attains the highest temperature of the furnace in the molten CaClz and transfers that heat upward. Thus, one of rthe reactants acts as the heat transfer medium and foreign gases are excluded.

It isof advantage to cause the phosphatic ores to become immersed, at least in part, in the fused calcium chloride in order to insure a good transmission of heat to the mass in reaction, this expedient notV checking the course of the reaction because the presence of fused calcium chloride in contact with the ores does not impede the action of the chlorine on the ores. It is probable that the CO liberated in the reaction above reacts in the upper and cooler part of the furnace according to the equation Cas (P04) z-|-6CO+ 6012-) 2POC13 -I-SCaClz-l- GC02 The electrical heating process according to the invention enables a precise and substantially uniform temperature to be maintained throughout the mass which is immersed in the fused calcium chloride, and in consequence, makes it possible to operate at a temperature substantially higher than those usually employed. The mean temperature may thus be brought close to the maximum temperature compatible with the continued resistance of the refractory walls of the reaction chamber to the action of the reducing mixture of chlorine and carbon. There is a considerable advantage in being able to operate at these higher temperatures because bothyield and speed are increased. At 800 C. the yield reaches 97% of that theoretically possible.

Using the heating method of the invention, with'the consequent easy and precise control of operations, and by employing as the refractories compact silico-aluminous products obtained by fusion in an electric furnace, the present applicant has been able to operate the process at 800 C., at which temperature all the calcium chloride formed in the reaction passes into the liquid state and flows freely, since the fusion temperature of pure calcium chloride is in the region of 770 C. The controlled removal of the calcium chloride is thus made easy and may be effected,

compared with its other dimensions, so that total Y absorption of the chlorine may be assured.` The -furnace has a lining 3 preferably formed from fused and compacted refractory materials such as, for example, the product, known under 'the il trade mark Corhart, which is a refractory, with a base of silica and alumina that is obtained by fusion in the electric furnace. The upper end of the furnace l is hermetically closed by a cover1 4 which has its inner face provided with a re- .fractory liningV 'and may be provided with a hopper through which a mixture of phosphate and carbon is introduced in amounts correspond- 'to remove the cap for inspections, or for actions that do not require the removal of the cover The cap il and the trough ill may be made of nickel or other resistant ware.

. The mixture of phosphate and carbon is support'ed on a grid 'l beneath which open nozzles 8 each delivering a current of chlorine which Vpasses through the grid to react with the mixture. AThese nozzles are made from a material,

such as cooled, nickel which is but slightly attacked by chlorine.

lThe current-supply electrodes 9 are mounted close to the bottom il) of the furnace, into which opens a pipe l l for the drawing off of the molten calcium chloride i2 under the control of a Siphon 20, maintained at about 800C C. by an auxiliary electrical heating. v

ln order to initiate the reaction, the temperature may be raised to 800 C. by some auxiliary heating means. When molten calcium chloride l2 has accumulated at the bottom of the Vat, electric current is passed through its mass and the auxiliary heating means is shut olf. The temperature of the bath i2 is thus maintained at a suitable valve by the heat generated in the calcium chloride, The siphon regulating the drawing off of the liquid from the bath l2 is vso arranged that the liquid rises above the grid 'l and immerses part of the mixture of phosphate and carbon.

The phosphate and carbon ought to be mixed together as intimately as possible, this necessitating fine subdivision of the materials. However, it is necessary to allow the chlorine to circulate through the mass, and it is consequently advantageous to make balls or briquettes by pressure from a ground mixture of natural tricalcium phosphate and wood charcoal. Only the minimum quantity of wood charcoal necessary to insure reaction with the phosphate should be eniplcyed and the formation of the balls may be 4 facilitated by adding ammonium phosphate as a binder. Charges are fed to the furnace through the cover Il, at a ratey equal to consumption in the reaction.

This invention is extensible to the preparation of other oxy-halides of phosphorous, but in pursuing the extension it must be remembered that different conditions of temperature and different reactivities occur. For instance CaFz melts at 1350 C. as compared to the 800 C, of CaCl2, and has a different reactivity. This requires the use of a different furnace and a close check upon corrosion rates.

The process proceeds above the temperature at which the metallic halide becomes molten, and the temperatureof highest eiciency may easily be'determined for each phosphatic raw material. This will also be affected by the particular halides employed in the reaction.

The following example is for the purpose of illustrationonly.V l v l Example An vagglomeration' -of natural calcium phosphate, coal of low ash content, and pitch having the following composition:

. A Kilos Phosphate f 700 Coal is ooked at 800 C., so as to obtain a porous mass free from volatile ingredients. The coke agglomerate is put in a furnace of the type-illustrated containing a bath of molten calcium chloride. 350 ou. in. of chloride is then admitted to the molten bath and 'passes up through the mass at high temperature Y and normal pressure. AThe computed useful yield was over 97% of the Weight of the phosphorus in the phosphate.

' This invention eliminates several treatments Vthat were required in processes of the prior art, Vsuch as washing to eliminate the CaClz that coated the reaction mass. It simplifies the problem of heat transfer byusing areactant gas as the transfer'medium. It is thermally economical, the molten CaClz serving as a heat reservoir the temperature of which is economically maintained by passing an electric current through it. The reaction proceeds more smoothly because it is vpossible to maintain a constant and high reaction temperature that tends to produce a uniform product. The product is uncontaminated by fthe contaminants found incertain prior art products.

As many apparently widely different embodimentslo'f the present invention may be made without departing from the spirit' and scope thereof, it is to be understood that the present invention is not limited to the'specic embodiment, except asedeiined in the appended claims.

What is claimed is:

l. ,The method'of preparing phosphorus oxychloride that comprises maintaining commingled Ycalcium phosphate and carbon above a pool of molten CaClz, passing an electric current through Vthe said pool to maintain it at a temperature lcirca 800 C., and passing chlorine gas through the pool into the reaction mass.

2,. The method of making phosphorus oxychloride that includes the steps of maintaining a pool of molten calcium chloride at the reaction temperature of chlorine gas and calcium phosphate by passage of an electric current through it, supporting .above and partly submerged in the pool a divided mass of calcium phosphate and carbon, and passing chlorine gas through the hot pool and into the mass at reaction temperature.

3. The method of producing phosphorus oxychloride that comprises heating and maintaining a pool of molten CaClz in the bottom of a furnace at a temperature of about 800 C., so as to supply the heat necessary for reaction, maintaining a charge of a mixture of calcium phosphate and carbon above the pool and in contact only with the upper portion of the pool, introducingchlorine into the pool so as to ascend therethrough and through the charge, and withdrawing the phosphorus oxychloride from the upper portion of the charge.

PAUL DUPONT.

REFERENCES CITED The following references are of record in the le of this patent:

6 UNITED STATES PATENTS Number Name Date 741,396 Chalmot Oct. 13, 1903 1,020,546 Fleming Mar. 19, 1912 1,169,817 Helfenstein Feb. 1, 1916 1,345,656 Yunck July 6, 1920 1,763,248 Moore June 10, 1930 1,884,656 Gelissen Oct. 25, 1932 2,089,689 Cornelius Aug. 10, 1937 2,290,961 Heuer July 28, 1942 2,354,753 Holder Aug. 1, 1944 2,386,529 Wilson et al Oct. 9, 1945 2,440,456 Alley et a1 Apr. 27, 1948 FOREIGN PATENTS Number Country Date 416,084 Great Britain Sept. 10, 1934 OTHER REFERENCES Industrial and Engineering Chemistry, Oct., 1933, pages. 1080-1083, Glass Lined Equipment in Chemical Industry. 

1. THE METHOD OF PREPARING PHOSPHORUS OXYCHLORIDE THAT COMPRISES MAINTAINING COMMINGLED CALCIUM PHOSPHATE AND CARBON ABOVE A POOL OF MOLTEN CACL2, PASSING AN ELECTRIC CURRENT THROUGH THE SAID POOL TO MAINTAIN IT AT A TEMPERATURE 